1. Field of the Invention
The present invention is concerned with the coding and transmission of images and patterns, and, more particularly, to the coding and transmission of information for telefax and for television, especially color television.
2. Description of the State of the Art
Facsimile equipment is split into standard groups in accordance with the transmission time. Groups 1 and 2 with point by point scanning have already been superseded by Group 3 equipment. The latter represents a digital transmission system in which the picture scanning points of equal brightness are brought together in an unbroken sequence and combined into a code word. Such methods are known as one-dimensional. The MHC method is an example of such a one-dimensional method. The two-dimensional process is built up on the same principle. In this case a reference line is first scanned and in the subsequent lines only departures from the reference line are coded. The MRC method operates in accordance with this principle. Then there is the MMR code, in which after a coded reference line a large number of subsequent lines are coded two-dimensionally. In run-length coding, for each number of picture points per line, a special binary code is determined for white and black, eg., 1 white=000111, 1 black=010, 2 white=0111, 2 black=11, . . . 20 white=0001000, 20 black=00001101000. Such coding goes up to picture point number 63. Then one starts again from the beginning with an additional section code word for white and black. For transmitting these coded numbers a phase-difference or amplitude-phase-difference modulation technique may be employed.
In gray-scale scanning, the gray values are divided into gray steps and converted in more or less close patterns of black and white dots. In this way, as is known from the Dither printing process, a corresponding gray step is taken in by the eye. In the coding of color images and patterns expensive processes have hitherto been necessary. To some extent similar to the coding in the NTSC, PAL and SECAM systems.